The Evolution of Hydras
by shiiki
Summary: After finding his stepson studying late at night, Paul devises a novel way to help Percy with school stuff.


**A/N:** This originally existed as two separate ficlets when I was participating in percyjacksonweek2k17, but it kind of fit together as a longer story overall. For those of you studying stuff ... I'm kind of interested in what you think about using fic to study. I feel like it ought to be a thing, but maybe that's just me.

OoOoOoOoOoOoO

The Evolution of Hydras

The kitchen lights were on when Paul got up in the middle of the night to use the bathroom.

He didn't think much of it at first—he lived with a teenager, after all, and they were a race prone to midnight refrigerator snack raids.

He was about to wander back to his bed when the muttering, pacing steps, and the soft clatter of something on the floor penetrated the sleepy fog over his mind. The numbers on his digital wristwatch glowed 3am—that miserable hour that was both too late at night and too early in the morning. If Paul were to guess, he'd say Percy hadn't gone to bed at all.

The kitchen was infused with a smell of coffee so concentrated, it nearly gave Paul a caffeine boost from inhaling it. Torn Nescafé sachets littered the counter, where Sally's French press lay on its side, coffee grinds spilling into the sink.

Percy was pacing the length of the kitchen, a beat up book with a rolled-back cover in one hand and a mug in the other. He kept tipping it to his lips, although no more liquid seemed to remain in it. Near the door, an innocent blue ballpoint pen—not the magical bronze one, Paul was relieved to note—rolled to Paul's feet. He bent to pick it up.

'Oh hey,' Percy said sheepishly. 'Sorry, didn't mean to wake anyone up.'

Paul handed him the pen. 'You didn't. I had to use the bathroom.' He gestured to the coffee marathon Percy had set up and a messy pile of papers on the kitchen table. 'What's up?'

Percy put his mug and book down. 'Got a test tomorrow. Er,' he cast a quick glance at his watch, 'today.'

'Last minute revision?'

Percy ran his fingers through his hair. It was already substantially ruffled, sticking up in the back as though he'd done this a hundred times throughout the night. 'I just can't get any of this. Tetchy's gonna fail me,' he muttered. His eyes widened as he remembered who he was talking to. 'Mr Tetley,' he corrected, with another rake of his fingers across his head.

Paul suppressed a grin. Charles Tetley was Goode High's twelfth grade biology teacher, and he'd come by the students' nickname for him fairly. He could easily have stepped straight out of that Roald Dahl autobiography with the old English schoolmasters, so straight-laced and irritable was his teaching style. Paul had made the mistake of asking the man to lunch once; he'd droned on obliviously about gene mutations and Punnet squares for a full hour, nearly setting Paul to snoring. If that was the way Tetley delivered his classes, it was no wonder Percy, who already found paying attention challenging under the best of circumstances, was struggling.

'I gotta pass this test,' Percy groaned. He sank into a kitchen chair and plopped his elbows on the table, hands tugging at his hair. 'Annabeth's gonna kill me if I don't graduate and go to NRU with her.'

Ah. That explained Percy's uncharacteristic motivation. Percy's formidable girlfriend had been over many an afternoon, their two heads bent over their homework as they struggled through the material together.

Annabeth could only do so much, though. Paul knew she faced the same learning challenges as Percy, although she did a remarkable job finding solutions to work around them. On Percy's textbook, between the paragraphs on natural selection and Darwinian theory, were multi-coloured stains that were evidence of her reward-each-paragraph-read-with-a-jelly-baby method.

Percy picked up his book again. His hands were shaking slightly, and Paul wondered if he'd progressed from jelly babies to espresso shots per paragraph.

He reached out and took the textbook from Percy's trembling hands. 'You're not doing yourself any favours if you go into the test without sleep. You need rest if you're gonna consolidate all this information.'

'I don't think I could sleep now if I tried,' Percy admitted, with yet another comb through his hair. 'I drank, like, a month's worth of coffee.'

Paul put his arm around his stepson's shoulders. 'At least come out and get some air,' he said.

He led Percy over to the tiny balcony. The cool night air, blustery with the promise of spring rainstorms, slapped Paul firmly awake, but it seemed to have a calming effect on Percy. Maybe it was the smell of it, fresh and forceful like an ocean gale blowing in from the Sound. Paul noticed the way Percy's body oriented itself automatically towards the breeze, leaning slightly into it as though yearning for the ocean of its origin.

 _Son of the sea god,_ Paul thought wryly. He remembered the first time he'd met Percy. Sally had warned him that her son didn't look anything like her, but he hadn't really believed it—there was always _something_ , even if it wasn't obvious—until he'd been standing in front of this dark kid with messy hair and features that made Paul wonder if Sally's ex had been of Mediterranean, or maybe Arabic descent. There was nothing of Sally in the contours of Percy's face, or his striking eyes. It hadn't been until Percy was introduced that Paul had spotted the faintest of resemblances—a single dimple when he smiled, the same firm handshake, a shared cadence and mannerism in their voices and postures.

The quizzical look Percy gave him now was most definitely Sally's, down to the way his head quirked to the side. 'You're looking pretty serious, Paul,' he said.

Paul shook his head. 'It's nothing.'

He looked up. The night was clear and cloudless, lit only by the stars.

'I can never place the constellations,' Paul remarked. 'It's like one of those connect-the-dot pictures, except without the numbers.'

The corner of Percy's mouth twitched. 'That's Ursa Major,' he said, tracing in the air with one finger. 'And Leo.'

'Indeed.' Paul scratched the day-old stubble on his chin, impressed. He hadn't imagined Percy to quite so knowledgeable about astronomy. It seemed quite an arcane bit of trivia for him to pick up.

Percy shrugged. 'Annabeth taught me. I—it's easier to remember stuff when it's connected to stuff you already know.' He made a face as he pointed to another constellation. 'The Hydra. Luckily that one only has one head.'

'Huh.' Paul drew his thumb and forefinger to meet under his chin. An idea was starting to form. He'd taught plenty of kids over the past fifteen years, and what had always stood out to him was how the same information presented in a completely different format could change their ability to understand it. 'Percy—if you ever need any help with school, you know I'm here, right?'

'Sure. I'm doing okay with the Hamlet paper, though. It's been lots clearer since you did the acting stuff with our class.' Percy rubbed his eyes. 'I may be failing Bio, but at least I'll pass English.'

'Don't give up, Percy,' Paul said. 'There's always one more class test. Even if you fall behind on this one, you can make it up.'

Percy grimaced. 'Doubt it. But thanks, Paul.'

Paul sent Percy off to bed, promising to clean up in the kitchen. The biology textbook was still lying open on the table. Paul stared at it for a long time.

Then he sat down at the table and began to read.

OoOoO

The problem with science textbooks, Paul thought, was that they insisted on presenting information in the driest way possible. Would it really kill the authors to inject at least some semblance of a narrative into the bare facts they attempted to shove down your throat?

Charles Tetley had been confused when Paul had asked to borrow a copy of the biology text he'd assigned his twelfth-graders, but he'd handed it over readily enough. Paul reread the notes he'd made on the chapter, double-checking them against the relevant paragraphs. Given the problems Percy was already having with the subject, it probably wouldn't make things too much worse if Paul messed up a few points, but it'd be much better if his analogies were accurate.

The fire drill during second period had been quite the godsend. Not for Paul—he didn't exactly appreciate the disruption to his class—but Percy had Biology second period. Which meant his test now had to be postponed to the following week.

It gave Paul a chance to see if his idea could help.

He spent his free periods and lunch break sketching. It had been years since he'd put together a comic (it was a hobby he hadn't indulged in since college) and it was quickly and clumsily drawn, but he thought it got the across well enough.

Paul hoped Percy would think so, too.

He caught up with his stepson that afternoon right after the last bell went. Percy was among the throng of seniors on their way out of the building when Paul tapped his shoulder.

'Oh hey, P—er, Mr Blofis.'

'Mind if I have a quick word?'

'Er, yeah, sure.'

'So, the fire drill today—'

Percy held his hands up immediately. 'I swear, that wasn't me.'

'No, no, that wasn't what I—' Paul sighed. The poor kid—he really was used to getting blamed for anything out of the ordinary. 'I just meant to say, I guess your Bio test didn't happen?'

Percy ran a hand through his hair. 'Yeah, it's next week now. Got a stay of execution.' His mouth twisted wryly. 'Too bad Annabeth went to Frisco this week. I could've used her help figuring out that evolution stuff'

'About that …' Paul held out his amateur comic.

'What's this?' Percy scanned the sketches first with bewilderment and then a glimmer of understanding. 'Hydra evolution?'

'Let me know if it helps.' Paul patted Percy's shoulder again and headed back to his office. He smiled when he turned back at the end of the corridor and saw Percy studying the comic as he left the school.

OoOoO

 _Everyone knows hydras have multiple heads. But they didn't always look that way._

 _When Poseidon made the first hydra from a magic green gem, it was a pretty normal dragon. Okay, yeah, normal's relative. But you know, breathes fire, spits poison—hey, it's a dragon, what do you expect? But one body, one head. Cut it off and it'd be dead, game over._

 _But what fun is that, right?_

 _Athena decided to 'improve' the design a little. She used her magic grey gems and came up with multi-headed hydras. Maybe she watched too much baseball, because she went with the three-strike policy: strike one, there's still a second head. Strike two, there's still the third. Strike three, sorry hydra, you're out._

 _So Poseidon had his single-headed hydras and Athena had her three-headed ones, and they didn't really mix until one day, a Poseidon hydra and an Athena hydra had a big adventure involving a daring escape from a demigod hero, saving each other and—okay, the details aren't important. The point is, they fell in love._

 _And had lots of little hydra babies … who all had only one head apiece._

 _Poseidon was pretty insufferable about that, since he was sure it must mean his hydras were better than hers. But he stopped boasting pretty quick when the grandkids came along and out of nowhere, a pair of single-headed hydras popped out a three-headed baby._

 _See, the thing is, hydras mix their gems when they mate. And when you mix green and grey, all you really see is green. But it doesn't mean the grey isn't there. It's still hiding under the surface, passed along down generations until one baby gets two grey gems. Without the green to overshadow it, the greys work their magic, and poof: three heads._

 _So the hydra population grew along merrily, eating heroes whenever they came along. For years, their numbers didn't change much—Poseidon's hydras seemed to be more numerous, since the mixed-gem kids always came out green and one-headed. But Athena kept telling him,_ wait and see.

 _Then the heroes got bigger and badder and started carrying sharp bronze weapons. They got better at killing hydras._

 _And Poseidon's hydras got hit the worst. I mean, one good slice was all you really needed to take them out._

 _Athena's hydras made it lots further, with their multiple heads. If they lost one, the others could still attack the hero. Their chances of survival were loads better._

 _So as time went on, the heroes killed more one-headed hydras than they did three-headed ones. After a while, the green gems that gave the hydras their single heads began to disappear._

 _Finally, only Athena's grey gems were left—which now kept producing three-headed hydras, unshadowed by the green gems that kept the multiple heads from developing. And today, demigod heroes must contend with all hydras having too many heads to fight._

OoOoO

Percy was sitting at the kitchen table when Paul got home that evening. He had the hydra comic in front of him, as well as his biology textbook.

'I don't know what my dad and Annabeth's mom would think of the story,' he said, 'but this finally makes sense.' He jabbed a finger at the biology text.

Paul hoped he hadn't inadvertently incurred the wrath of two Greek gods. He hadn't really thought about that when he was sketching his Darwinian analogy. Maybe they'd forgive him; he was only trying to help their kids out, after all.

Percy pointed to a few highlighted passages in his textbook, cross-referenced against Paul's comic panels. 'The gems are genes. And the heroes are selection pressures. Right?'

Paul beamed. 'Right.'

'This is brilliant!' Percy said. 'Do you think you could do this for, like, history and chem and—'

'Whoa.' Paul held up his hands. 'I'm not that great an artist.' Not to mention he'd have his work cut out for him trying to figure out all those subjects. But then, this was what it meant to be a teacher, wasn't it?

No, scratch that. This was what it meant to be a _dad._

'But we can talk about it,' he said.

A wide grin spread across Percy's face. 'There's one thing you should know, though.'

'What's that?'

'You do know hydras _regenerate_ heads, right?'

Paul laughed. 'Well, maybe you can give me a crash course on monster physiology in return.'

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 **A/N:** So ... what did you think? I'm fairly sure I'd've loved studying a lot more if I could just read a ton of fic that worked in the subject matter. Anyone with an exam coming up want to challenge me with a study subject to fic about? (Can't promise I'll know enough to attempt it, but I'd love to try.)

(I will admit freely that when I was studying for a Brain and Behaviour exam two years ago I basically wrote a HP fic about Tonks studying the lycanthropic brain because I was sick and tired of writing another practice essay for the exam.)


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